1. Field of the Invention
The invention relates to a monolithically integrated semiconductor circuit which includes I.sup.2 L cells and further circuit parts, the supply voltage of which is a multiple of the supply voltage required for the operation of the individual I.sup.2 L cells, in which a corresponding number of I.sup.2 L cells are accordingly connected in series in chain-fashion with respect to the two supply terminals of the circuit which furnish the supply voltage for the circuit and are acted upon by an operating potential each, in that the injector of an I.sup.2 L cell forming a first chain link is tied to the first supply terminal of the circuit; the emitter of the transistor of the I.sup.2 L cell forming the first chain link is tied to the injector of a further I.sup.2 L cell forming the second chain link; the injector of an I.sup.2 L cell forming the third chain link is tied to the emitter of the transistor of the I.sup.2 L cell forming the second chain link, in which the chain is finally completed, using further I.sup.2 L cells connected in the same manner to the respective preceding chain link and forming a respective chain link, by the I.sup.2 L cell forming the last chain link, in that the emitter of this I.sup.2 L cell is connected to the second supply terminal designated as VB* in the figures of the circuit which carries the reference potential of the circuit, while the injector of this last I.sup.2 L cell is directly connected to the emitter of the transistor of the I.sup.2 L cell forming the next to the last chain link.
2. Description of Prior Art
Details regarding I.sup.2 L cells may be found, for instance, in "Valvo Berichte", Volume XVIII, No. 1/2, (1974), pages 215 to 236. As is well known, the individual I.sup.2 L cells include a combination of a vertical npn transistor, with an injector constructed as a lateral pnp transistor. The base of each is surrounded by the emitter and the collectors of which each is surrounded by the base, the collector forming the signal output and the base terminal the signal input. The base of the lateral transistor is identical with the emitter of the vertical transistor and the collector of the lateral transistor is identical with the base of the vertical transistor.
The supply terminals of the I.sup.2 L cells are represented by the emitter of the lateral transistor, i.e. the injector, and the emitter of the vertical transistor. Since the values of binary potential states of an I.sup.2 L cell are U.sub.H =0.7 V and U.sub.L approximately--0.1 V and therefore a voltage excursion of about 0.8 V is needed, the problem arises, in a monolithic combination of I.sup.2 L cells with other digital circuit parts, of matching the I.sup.2 L cells to the supply voltage required for the overall circuit which in the case of TTL circuits is approximately 5 V, while the I.sup.2 L cell requires a voltage U.sub.I for the injector of about 0.8 V. For this reason, the construction of the I.sup.2 L circuits is carried out in accordance with the manner described hereinafore to build up a network of I.sup.2 L cells, so to speak. Pertinent details may be found, for instance, in a paper by K. Kameko, T. Okabe and M. Nagata from the literature reference "IEEE Journal of Solid State Circuits" (April 1977), SC12, pages 210 to 212.
One problem arising in such I.sup.2 L combinations is already solved in German Published Non-Prosecuted Application DEOS No. 27 23 973, using an auxiliary circuit. The price of this solution, however, is a considerable amount of circuitry.
On the basis of the description given hereinafore, the available supply voltage is subdivided by the individual links of the chain of I.sup.2 L cells connected between the two supply voltage terminals of the integrated semiconductor circuit into equal partial voltages, each of which is allocated as the supply voltage to the respective I.sup.2 L cell forming the respective chain link. The individual partial supply voltages, however, are assigned to staggered values of the potential at the emitters of the transistors of the individual I.sup.2 L cells. Since the individual I.sup.2 L cells interact as a rule with other I.sup.2 L cells and these I.sup.2 L cells are likewise connected between the two supply terminals as links of a chain of I.sup.2 L cells, with respect to the supply voltages that serve for setting their operating point, it may happen that one I.sup.2 L cell controls further I.sup.2 L cells, which are not acted upon exclusively by the same values of the potential present at their injector and the potential present at the emitter of its transistor as is the controlling I.sup.2 L cell. Thus, a cell to be controlled can be acted upon by supply potentials which are either closer to the first supply potential or closer to the second supply potential, i.e. the reference potential, than the I.sup.2 L cell under consideration. If the controlled I.sup.2 L cell is closer to the supply potential of the overall circuit with respect to its two supply potentials than the cell under consideration, this control is called an up control. It does not involve special problems and can therefore be ignored in the further consideration.
If, however, the controlled I.sup.2 L cell is closer to the second supply potential, i.e. to the reference potential of the circuit, with respect to its supply potentials, concern is raised about the so-called down control. As has already been set forth in the German Published Non-Prosecuted Application DEOS No. 27 23 973, down operation, i.e. controlling an I.sup.2 L cell belonging to a lower potential level or stack plane by an I.sup.2 L cell belonging to a higher I.sup.2 L cell goes along with a delay of the switching operation, because it then takes the transistor of the controlled I.sup.2 L cell a particularly long time to be ready for operation again when a signal provided by the controlling I.sup.2 L cell decays.